The present invention relates generally to linear position sensors, and, more particularly, in one embodiment, to a linear position sensor capable of providing a quadrature output signal that can comprise two square wave signals that are ninety degrees out of phase.
Sensors are utilized to indicate the value of a measured parameter, such as position, temperature, pressure, rotation, velocity, and the like, by providing an output signal. As an example, a linear position sensor can indicate the position of a movable mass. For example, such linear position sensors can indicate the position of a movable machine element, the location of a movable piston in a cylinder, or the level of a movable liquid in a container.
A magnetostrictive linear position transducer is a type of linear position sensor where a phenomenon known as magnetostriction is utilized to determine the position of the movable mass. In particular, in one such sensor, a control circuit transmits an interrogation signal along a wire that is adjacent the length of a waveguide, the waveguide being made from a magnetostrictive material. A magnet is movable along the waveguide and is connected to or otherwise follows the movable mass. When the interrogation signal reaches the location of the magnet, a magnetostrictive effect is created in the waveguide causing a strain wave and a electromagnetic wave to be generated and to travel along the waveguide. A detector is provided near the end of the waveguide to detect when one of these waves has reached the end of the waveguide and to cause an electrical return signal to then be generated.
A circuit or processor can then compute the amount of time elapsed between the sending of the interrogation signal and the generation of the return signal. The amount of time computed is directly proportional to the distance of the magnet from the coil end of the waveguide. The speed at which the magnetostrictive wave will travel along the waveguide is known (and is a function of the material of the waveguide). Accordingly, multiplying the time computed by the known magnetostrictive speed constant will result in the distance of the magnet along the waveguide. The distance can then be provided as an absolute value in an analog or digital format to a control device, such as to a programmable controller or the like.
However, certain control systems are configured to be used with sensors that provide incremental signals, such as quadrature signals for example. A linear encoder is one sensor device that typically provides a quadrature output signal which indicates the change in position of the movable element, rather than the absolute position of that element. In particular, such a device can provide a pair of square wave signals which are approximately ninety degrees out of phase. Each rising and falling edge of these two square wave signals represents an increase or decrease in position. The quadrature signals are provided to a control system, and a counter in the control system can keep a running tally of the increases and decreases, so that it continually has knowledge of the position of the movable element. The counter can increase or decrease the count according to the rising and falling edges of the two signals (the A and B signals). Whether the A signal leads or lags the B signal indicates whether the position is increasing or decreasing and whether the counter should increase or decrease its count. Using the position count, the control system can then control the process or machine at hand.
While many magnetostrictive position sensors provide digital or analog output signals, it is desirable to provide a magnetostrictive position sensor that provides a quadrature output such that it can be utilized with those control devices and control systems that require such signal formats as inputs. In particular, it is desirable to provide such a quadrature output sensor and other quadrature output devices that are accurate, that are low in cost, that provide selectable or programmable features, that minimize control circuit components, that indicate when errors have occurred, that provide an output representing a recent measurement, that account for waveguide variance, and/or that are easily modified as desired. Moreover, it is desirable to provide a quadrature output linear position sensors and other sensors that are easily calibrated.
At least one embodiment of the present invention provides an improved quadrature output sensor.
Furthermore, at least one embodiment of the present invention provides a quadrature output sensor that is accurate, low in cost, provides selectable features, minimizes control circuit components, can indicate when errors have occurred, provides an output representing a recent measurement, accounts for waveguide variance, is easily modified as desired, and/or is easily calibrated.
In particular, a linear position sensor is provided comprising a magnetostrictive waveguide, a signal detector configured to generate a return signal from a magnetostrictive response of the waveguide, and a control module configured to provide a position output signal in response to the time delay between the interrogation and return signals. In addition, the sensor comprises a microcontroller in communication with the control module, and a program configured to be executed by the microcontroller. The program is adapted to determine a number of quadrature pulses to be provided in response to the change of the position output signal and to generate that number of quadrature pulses at two outputs of the controller by providing approximate square wave signals at those outputs. The square waves provided at the outputs are approximately ninety degrees out of phase from one another.
In addition, a method in a sensor is provided for generating incremental output signals indicating the change in a parameter. The method comprises providing a signal representing the value of the parameter, and using a program to determine a number of transitions to provide based upon the change in the value of the parameter. The method further comprises using the program to switch at least one incremental output signal based upon the number of transitions determined, such that the number of transitions in the incremental output signal represents the change in parameter.
Moreover, a programmed method in a sensor is provided for generating quadrature output signals indicating the change in a measured parameter. The method comprises determining a transition count based upon the change in the measured parameter, and determining the direction of the change in the parameter. The method further comprises generating a pair of quadrature pulse signals such that the number of transitions in the quadrature pulse signals is substantially equal to the transition count, and such that the phase of the pulse signals is offset based upon the direction determined.
In addition, a method is provided for providing output signals in a quadrature output device. The method comprises providing a measurement signal indicating the value of a measured parameter, and generating a pair of signals having a number of transitions, the number of transitions in the signals having a relation to the measurement signal. The method further comprises detecting whether an error has occurred, and, if an error has occurred, causing a simultaneous transition of the pair of signals.
Furthermore, a method for providing output signals from a sensor is provided. The method comprises receiving at least one input from a user indicating a user selection, modifying a program setting based upon the user selection, and determining the value of a measurement parameter. The method uses the program to generate a pair of signals having a number of transitions, the number of transitions in the signals having a relation to the measured parameter.
Moreover, a method for calibrating a sensor is provided. The method comprises testing the sensor to determine calibration factor data, and connecting a calibration device to at least one sensor input that is normally used to receive a command signal from an external control device. The method also comprises loading calibration factor data from the calibration device over the at least one sensor input.
Furthermore, a method is provided for producing a quadrature output from a position transducer having a magnetostrictive waveguide. The method comprises determining a time to produce an interrogation signal such that a response signal will be received from the waveguide prior to the receipt of a strobe signal from a control device. The method further comprises generating an interrogation signal at the determined time, and receiving a response signal, wherein the time difference between the interrogation signal and the response signal is proportional to the measured position. The method further comprises receiving a strobe signal from a control device, and, in response to the strobe signal, generating a quadrature output signal based upon the time difference such that the quadrature output signal represents the change in the measured position.
Still other advantages and aspects of the present invention will become apparent to those skilled in this art from the following description wherein there is shown and described details of illustrative embodiments simply for the purposes of illustration and for describing currently contemplated best modes. As will be realized, other variations and embodiments can be provided without departing from the scope of a given claim, and particular aspects, details, embodiments, principles, and advantages mentioned should not be viewed as restricting a given claim. Accordingly, the drawings and descriptions are to be regarded as illustrative in nature and not restrictive in nature.